The present invention generally relates to removal of toxic metal and cyanide values from waste waters. One aspect of the invention relates to treatment by means of a multi-level ion exchange resin bed having a strong base anion exchange resin layer, a weak acid cation exchange resin layer, and a strong acid cation exchange resin layer, and regeneration of such multi-level bed, while another aspect of the invention relates to recovery of cyanide values from acidic waste waters such as those that have been loaded with cyanide values during regeneration of an ion exchange resin bed, the cyanide recovery means including a circulation reactor having an inclined passageway for reacting hydrocyanic gas with a caustic fluid to form and recover cyanide salt. The invention is particularly suitable for treatment of waste waters from commercial plating baths, or other waste waters having a significant concentration of cyanide values, heavy metals, or toxic metals.
Various systems have been devised through the years for the utilization of ion exchange beds to treat waste waters, such as those described in U.S. Pat. No. 2,666,741, No. 3,617,558 and No. 4,009,101. These patents as well as other publications such as U.S. Pat. No. 3,455,819 provide detailed teachings of several approaches that can be taken in regenerating multi-level resin beds containing both cation resin beads and anion resin beads, although such systems tend to develop channeling problems within the resin bed due to uneven or imprecisely controlled flows during the various regeneration steps. Also, these publications do not teach an efficient, on-stream system for removing and recovering cyanide values in a form suitable for re-use within a plating bath.
By the present invention, a multi-layered ion exchange resin bed generally maintains its multi-layered characteristics, with both anionic and cationic resin bead layers remaining within their generally discreet layers, as the bed is in its loading stage and during most phases of its regeneration stage, such being accomplished by sequenced movement of volumes of rinsing liquids, acidic regeneration solutions, basic regeneration solutions, and air in order to control bed disturbance while at the same time thoroughly and rapidly regenerate the multi-layered bed, which bed is particularly well suited for removal of multivalent, especially bi-valent, heavy metal ions as well as cyanide values from plating bath waste streams. In another aspect of this invention, the cyanide containing rinsing streams flowing off of the multi-layered bed are subjected to treatment to react the cyanide values with caustic in order to recover cyanide salt liquor suitable for re-use within a cyanide plating bath.
It is, therefore, a general object of the present invention to provide an improved system for removal of toxic metal and cyanide values from waste waters.
Another object of this invention is an improved ion exchange processing method for efficiently and thoroughly removing multivalent metal values and cyanide values from waste streams of metal plating baths.
Another object of the present invention is an improved ion exchange treatment system having multiple treatment vessels, whereby substantially continuous waste water treatment can be accomplished by taking one or more of the vessels off stream for regeneration while at least one other vessel is treating the waste water flow.
Another object of this invention is an improved system for regenerating a multi-layered ion exchange resin bed including a strong anionic resin as well as both a weak and a strong cationic resin without excessive movement of or extensive damage to the resin beads within the various layers.
Another object of the present invention is an improved apparatus and method for recovering cyanide values within acidic regeneration wastes from ion exchange treatment of waste waters.
Another object of the present invention is an improved method and apparatus whereby cyanide and metal complexes within plating bath wastes are treated first in an ion exchange system to break up the complexes and form hydrocyanic acid, and second in a reactor to remove the hydrocyanic acid from such ion exchange treated wastes in order to recover the cyanide values in the form of cyanide salt.
Another object of the present invention is an improved apparatus and method for reacting gaseous hydrogen cyanide with a caustic solution to form a cyanide salt solution.